A soybean curd, being nutritious and manufactured by coagulating soybean protein is a food which has been eaten by many people. Thus, the soybean curd is manufactured by speciality manufacturers in large amounts and sold in supermarkets and the like in large quantities at less expensive price. However, the packed soybean curd sold in large quantities is eaten after a time passes from the time it was manufactured, the taste, deliciousness, smell, and feeling in the mouth, such as on the teeth or tongue thereof are inferior to those of a fresh soybean curd manufactured by soybean curd stores in town. Consequently, since a small, traditional soybean curd stores in town supply a fresh and tasteful soybean curd to dining tables of homes, there exists a soybean curd which is manufactured by hand using a conventional method, although the quantity thereof is small.
Incidentally, a soybean curd is manufactured by grinding soybeans immersed in water; boiling the thus obtained ground soybeans; obtaining a "go" (bean juice which is obtained by grinding soybeans immersed in water or thereafter by boiling ground soybeans) by extracting soybean protein from the boiled soybeans; obtaining soybean milk by separating an okara (solid soybean curd lees) as a solid matter from the bean juice (or nigo which is boiled bean juice); cooling the thus obtained soybean milk; mixing the cooled soybean milk with a coagulant such as a "nigari" (magnesium chloride which is usually used as an aqueous solution) to thereby obtain a mixture of the soybean milk and the nigari; and coagulating the soybean protein by heating the mixture. Calcium sulfate and the like are used as the coagulant of the soybean milk, in addition to the nigari.
As described above, the soybean curd is a very popular food. However, to make a soybean curd having a good taste and a good smell, not only high speciality is required in a technique for manufacturing soybean milk of high quality as a raw material of the soybean curd and in a technique for adding a nigari to the soybean milk and coagulating the soybean milk but also the entire soybean curd manufacturing steps from a step of boiling ground soybeans to a step of coagulating the soybean milk must be successively carried out. As a result, a small soybean curd store is compelled to work from an early morning without a rest to supply a fresh and tasteful soybean curd so that it is in time for family breakfast.
To produce the soybean milk as the raw material of the soybean curd, ground soybeans are conventionally boiled in a dedicated bean-juice-manufacturing caldron. The bean-juice-manufacturing caldron used to the manufacture of soybean milk, a soybean curd and membrane-like soybean curds ("yuba") comprises a cylindrical caldron main body having closed upper and lower ends, a charge port disposed at lower portion of the caldron main body for charging a raw material of bean juice such as ground soybeans to which water is added or the heated ones thereof, a discharge port disposed at upper portion of the caldron main body for discharging the raw material after it is processed in the caldron, and a steam injection pipe having a plurality of injection ports simply formed therethrough and installed in interior of the caldron main body.
Steam used in the conventional bean-juice-manufacturing caldron is air-containing steam obtained by simply heating ordinary water. The ordinary water contains oxygen in an amount of 8-10 ppm.
In the conventional bean-juice-manufacturing caldron, the steam injected from the injection ports of the steam injection pipe is injected in a radial direction. The steam injected in the radial direction collides against the inner peripheral wall of the caldron main body and lose their motion energy so that the flow rate of the streams is reduced. Therefore, the steam having the reduced flow rate cannot sufficiently turn and flow into the space located backward of the injection ports in the caldron main body and the steam only moves upward in the caldron main body. As a result, the steam is in good contact with the raw material of bean juice or the heated one thereof (hereinafter, they are referred to as raw material of bean juice as a whole) which is located in the vicinity of the radially injecting passages of the steam which is directed radially from the injection ports so that the raw material of bean juice located at the position is sufficiently heated with the heat of the steam. However, since the steam comes into contact with the raw material of bean juice in a small quantity which is located in the space backward of the injection ports of the caldron main body, the heat of the steam is not sufficiently transmitted to the raw material of bean juice located at the backward position. Thus, the raw material of bean juice cannot be heated with a necessary quantity of heat. As a result, a part of the raw material of bean juice is sufficiently heated and the other part thereof is insufficiently heated, whereby the raw material of bean juice is unevenly boiled. There is caused thereby a problem that soybean milk of good quality cannot be obtained from the unevenly boiled bean juice.
In the conventional bean-juice-manufacturing caldron, since steam cannot be uniformly and sufficiently supplied to the raw material of bean juice, the steam cannot sufficiently transmit their heat to the raw material of bean juice. Accordingly, a large quantity of the steam stay in the upper portion of the caldron main body while holding a sufficient quantity of heat at high temperature and increase the pressure of the upper portion of the caldron main body as a residual steam. Thus, there arises a problem that the raw material of bean juice is pushed out into the discharge port of the caldron main body in a quantity larger than necessary, the feed of the raw material of bean juice in the caldron main body cannot be properly controlled, the raw material of bean juice has a portion to which the heat of the stream is transmitted well and which is sufficiently heated and a portion which is insufficiently heated, whereby the raw material of bean juice is unevenly boiled, bean juice of good quality cannot be produced and thus a soybean curd of good quality cannot be manufactured.
Incidentally, when a soybean curd is manufactured by coagulating soybean milk by adding a nigari (magnesium chloride) as a coagulant thereto, the nigari can well extract sweetness and flavor of soybeans. However, since the coagulating reaction proceeds too promptly, this process cannot be often performed successfully. Thus, not only a sophisticated technique is required to mix the nigari with the soybean milk but also a speed at which the nigari performs a coagulating reaction must be controlled by minutely monitoring a coagulation state thereof and controlling the temperature thereof. Therefore, conventionally, soybean milk is cooled so as to be slowly coagulated, and after a nigari is well mixed with the soybean milk, the thus obtained mixed solution is slowly heated with steam or in a water bath. Thus, there is a problem that 1-2 hours are necessary to the heating of the mixed solution, which is very inefficient. Further, since a long time is necessary to the heating of the mixed solution, the outside portion of a soybean curd is exposed to a very high temperature as compared with the inside portion thereof and heat is excessively applied to the outside portion of the soybean curd, from which a problem arises in that the outside portion of the soybean curd is heated secondarily and tertiarily and the water keeping property of the thus obtained soybean curd becomes poor.
As described above, when soybean milk, which is obtained by separating an okara from an insufficiently heated bean juice (of low quality), is used in the mixture of the soybean milk with a coagulant such as a nigari and the like which requires the sophisticated technique, it is still more difficult to make a soybean curd of high quality because the soybean milk is also unevenly manufactured. This is because that soybean milk obtained from a uniformly and sufficiently heated bean juice (of high quality) not only promptly reacts to a coagulant but also is mixed therewith quickly as compared with the unevenly manufactured soybean milk. That is, when a coagulant such as a nigari or the like is added to soybean milk manufactured from an unevenly cooked bean juice in the manufacture of a soybean curd, the coagulant is concentrated at the portion of the soybean milk which was obtained from the sufficiently heated portion of the bean juice before a coagulanting reaction occurs to the entire soybean milk, the soybean milk is reacted to the coagulant promptly, and thus the coagulant cannot be uniformly mixed with the entire soybean milk. As a result, there is a problem that a soybean curd of high quality having elasticity and a sufficient water keeping property cannot be still more manufactured.
Incidentally, since steam is obtained by simply heating ordinary water in the conventional bean-juice-manufacturing caldron, it cannot be avoided for air to be mixed with the steam when it is manufactured so that oxygen is contained in the steam. When a raw material of bean juice is boiled with the steam in which the oxygen is mixed, it is also mixed with or dissolved in soybean milk obtained by separating an okara from bean juice. Thus, there is a problem that the soybean milk is deteriorated in a very short period of time and a soybean curd of high quality cannot be manufactured from the soybean milk as well as a lot of porosities are formed in the soybean curd due to the dissolved oxygen and the taste thereof becomes deterigated. To cope with this problem, a fresh soybean milk must be used at once for the manufacture of a soybean curd. Thus, a soybean curd of high quality is manufactured only by a speciality manufacturers and it is impossible to supply a fresh soybean curd to homes and eating houses.
Further, soybean milk is an excellent drink which does not cause atopic dermatitis and allergy symptoms different from a cow's milk regardless of that it is as nutritious as the cow's milk and less expensive. However, a fresh soybean milk manufactured from the conventional bean-juice-manufacturing caldron cannot be stored for a long time unless it is sterilized at high temperature. However, when the soybean milk is sterilized at high temperature, it is somewhat denatured and the deliciousness characteristic to the soybean milk is lost. Consequently, there is also a problem that a fresh soybean milk having deliciousness and a good taste is sold only in the vicinity of a small-scaled speciality soybean curd manufacturers in a very small quantity and cannot be freely distributed in a market.
A leading subject of the present invention is to solve the above problems of the conventional techniques and to provide soybean milk of high quality, soybean packs into which the soybean milk of high quality is filled, soybean milk manufacturing method capable of manufacturing the soybean milk of high quality and soybean milk pack manufacturing method of manufacturing the soybean milk packs.
The soybean milk of high quality can be obtained by separating a solid matter from a uniformly boiled bean juice of high quality obtained by using a novel caldron. The soybean milk can be stored without the need of high temperature sterilization while keeping the sweet taste, smell, deliciousness and freshness characteristic to the soybean milk; is less deteriorated even if it is stored; and can be drunk as a drink as it is, in addition to that it is used as a raw material of a soybean curd of high quality. The soybean milk packs can be stored for a long time; can be handled easily; and can be supplied to an ordinary home and an eating house as well as to a speciality soybean curd manufacture.
Another subject of the present invention is to provide a soybean curd manufacturing method capable of supplying a just cooked and fresh soybean curd of high quality which can be manufactured easily in a short time by a nonprofessional in ordinary homes and eating houses, in addition to speciality soybean curd manufacturers, using the soybean milk of high quality and the soybean milk packs. The soybean curd made by the method is of high quality, namely, fresh, tasteful, delicious and mild felt on the tongue and has a good water keeping property without porosities formed therein.